Reactor for depositing a layer on a moving substrate

ABSTRACT

A solar cell having a layered structure with improved characteristics can be manufactured in plasma assisted CVD at a high rate deposition. In one aspect, separators are arranged between discharge electrodes to control a distribution of the composition of a reaction gas in a reaction chamber, giving a desired composition profile of a layer in the direction of the layer thickness. In another aspect, a grid electrode is inserted between a substrate and one of discharge electrodes only near an entrance portion thereof so that a high power can be applied to discharge electrodes to increase a deposition rate without plasma damage to an interface between a layer to be deposited and an underlying substrate. In a further aspect, an electric-field-adjusting means such as a metal wire is provided with an opening of a mask arranged between a substrate and one of the discharge electrodes for controlling the quality and layer thickness of a layer to be deposited. This electric-field adjusting means makes the electric field distribution uniform in the mask opening, thereby preventing a nonuniformity of the characteristics of a deposited layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reactor for manufacturing asemiconductor device, and particularly, to a reactor for depositing alayer on a moving substrate by plasma assisted chemical vapor deposition(PACVD), which is especially suitable for manufacturing a solar cell.

2. Description of the Related Art

The processes for manufacturing a semiconductor device by depositing asingle or a plurality of thin semiconductor layers onto a substrate in aplasma atmosphere by chemical vapor deposition (CVD) are well known; forexample, a process for manufacturing an amorphous silicon solar cell bya glow discharge decomposition of silane (SiH₄) gas. Note, a typicalamorphous silicon solar cell has a substrate/n-type microcrystallinesilicon/i-type amorphous silicon/p-type microcrystalline siliconstructure. Among the known processes, a process in which a substrate iscontinuously moved in a CVD plasma discharge atmosphere is consideredsuitable for the efficient manufacture of a thin semiconductor layer ona large scale.

This process can be carried out by the following two methods: The firstis the load lock method in which a single, or if necessary a pluralityof, completely isolated reaction chamber(s) for plasma discharge is(are) arranged between a loading chamber and a take-up chamber, andsubstrates are carried on a carriage and transferred through eachchamber, including the reaction chamber, and a layer is deposited ontothe substrates during the stay in the reaction chamber(s). The second isthe roll-to-roll method in which a substrate is supplied as a form of arolled-up strip which is transferred from a supply roll chamber to atake-up-roll chamber, between which a single, or if necessary aplurality of, reaction chamber(s) for plasma discharge is (are) arrangedand a layer is deposited onto the substrate while it is continuouslymoved through the reaction chamber(s).

In an advantageous process, a p-i-n structure of a solar cell ismanufactured in successively connected reaction chambers through which asubstrate, preferably a rolled-up strip, is continuously moved, and inwhich p-type, i-type, and n-type layers are successively deposited.

In a process for depositing semiconductor layers onto a substrate byplasma discharge CVD (plasma assisted CVD), if a plurality of layershaving different compositions or levels of doping impurity are to beformed, the reaction gas is changed for each layer in a reactionchamber, or a plurality of reaction chambers, in which differentreaction gases are used, and a substrate is transferred successivelythrough the reaction chambers. This is because a single reaction chamberinvolves an almost uniform composition of plasma gas and does not allowan appropriate spacial distribution of the composition of the plasmagas. Therefore, if a desired spacial distribution of the composition ofthe plasma gas could be formed in a single reaction chamber, a pluralityof layers having different composition or levels of doping impuritycould be formed only by moving a substrate through a plasma gas havingsuch a desired spacial distribution of the compositions in a singlereaction chamber, thus allowing the process and apparatus ofmanufacturing the plurality of layers to be simplified.

A disadvantage when a plurality of layers having different compositionsor doping levels are to be formed consecutively on a substrate, is thatplurality of reaction chambers becomes necessary because a reaction gashaving a each required composition must be fed into each of the reactionchambers.

When a plurality of reaction chambers are used in the roll-to-rollmethod, the respective reaction chambers are not completely separatedand independent, but are interconnected by a passage along which thesubstrate is moved, and as a result, it is inevitable that the reactiongases in neighbor reaction chambers will be intermixed by movement of asubstrate through the passage connecting the reaction chambers. As theabove intermixing of reaction gases causes a deterioration of thecharacteristics of a device which comprises a plurality of layers havingdifferent compositions, proposals have been made to form a predetermineddirectional gas flow along the substrate passage connecting the reactionchambers (see Japanese Unexamined Patent Publication (Kokai) No.58-216475); to provide a buffer chamber between the reaction chambers,by which each reaction gas in the reaction chambers is isolated to apredetermined level by evacuation (see Japanese Unexamined PatentPublication (Kokai) No. 59-34668); and to provide a slot interconnectingthe reaction chambers and establish a gas flow from the slot into areaction chamber at a rate sufficient to maintain a ratio of 10⁴ ofconcentration between the reaction chambers (U.S. Pat. No. 4,438,723).However, in these methods, once a reaction gas penetrates a neighboringreaction chamber having a different reaction gas composition beyond theisolation means (the buffer chamber), the penetrated reaction gasdiffuses throughout the entire neighbouring reaction chamber and becomesuniformly distributed in that reaction chamber thus there is no way ofcontrolling the distribution of the composition or the level of dopingimpurity in a direction of the layer thickness at the interface ofsuccessive deposited layers, for example, to obtain a graded junction ora stepped junction. It is known that a specific profile of a dopantlevel in an i-type silicon layer may improve the cell characteristics ofan amorphous silicon solar cell having a p-i-n structure (For example,"Technical Digest, 1st International Photovoltaic Science andEngineering Conference Nov. 13-16/1984", P-I-16, pp. 187-190).Therefore, the capability to control the profile of a doping level in adeposited layer is obviously advantageous in the manufacture of anamorphous silicon solar cell.

One object of the present invention is to solve the above-mentionedproblems of the prior art and to allow the control of a spacialdistribution of a reaction gas in a single reaction chamber duringplasma discharge CVD.

Another object of the present invention is to provide, for example,layers having a desired interface profile such as a graded or steppedjunction.

In the manufacture of a solar cell on a large scale, the deposition rateshould be increased. To accelerate the deposition rate, the glowdischarge power is increased under the supply of sufficient reaction gasto increase the concentration of the active species. However, in thatmethod, the increase of the glow discharge power causes an increase ofthe kinetic energies of the charged particles, causing so-called plasmadamage, for example, damage to the surface of the substrate or the layerdeposited on the substrate by bombardment of the charged particles, andas a result, deterioration of the characteristics of a device comprisinga deposited layer. This disadvantage is particularly noticeable when ani-type semiconductor layer is formed on a p-type or n-type semiconductorlayer in the manufacture of an amorphous silicon solar cell.

A further object of the present invention is to solve this problem ofthe prior art and to allow a fast deposition of a layer by plasmadischarge CVD without plasma damage.

An arrangement of the thickness of a layer is necessary in thedeposition of a layer on a moving substrate in plasma discharge CVD. Tothis purpose, a mask is sometimes provided to control the amount ofplasma reaching the surface of a substrate so that the thickness of adeposited layer is arranged. A mask is also used for depositing a layerin a desired pattern. However, the inventors found that this arrangementof a mask causes variations in the quality of the depositedsemiconductor layer, between the edge portion and the central portion ofthe opening of the mask. When a microcrystallized amorphous siliconlayer was deposited in plasma discharge CVD with a mask, it was foundthat a portion of the deposited layer near the edge of the opening ofthe mask had been microcrystallized but the deposited layer near thecenter of the opening of the mask was amorphous and the conductivity ofthe deposited layer gradually decreased from the edge toward the centerof the layer.

Therefore, an object of the present invention is to solve this problemand to allow a deposition of a uniform layer even when a mask is used tocontrol the quality or thickness of a layer to be deposited.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided a reactor for depositing a layer on a moving-substrate, saidreactor comprising: a reaction chamber having opposite ends; oppositeelectrodes for electric discharge arranged in the reaction chamber, thesubstrate being moved between the opposite electrodes from one end tothe other end of the reaction chamber; a means for feeding a reactiongas to the reaction chamber; a means for separating at least the spacebetween the moving substrate and one of the opposite electrodes into aplurality of regions and substantially preventing a diffusion of a gasbetween the separated regions; and a power source for supplying a powerbetween the opposite electrodes to excite the reaction gas to a plasmastate; whereby a layer having a modified depth composition profile isdeposited on the substrate.

This aspect of the present invention was accomplished by finding thatarranging of the separators perpendicularly between discharge electrodesfor preventing an interdiffusion of gases in the separated regions doesnot disturb the glow discharge, thus allowing a stable deposition, andthat by restriction of the passage of a reaction gas between theseparated regions to a narrow area adjacent to the surface of asubstrate, and by locating a gas inlet and a gas outlet in a directionof movement of the substrate, the distribution of the composition of thegas can be controlled in the direction of movement of the substrate.

The separating means used in the present invention is not particularlylimited as long as it acts as a barrier to a gas, but is preferably madeof a material which is not damaged by plasma, including, for example,stainless steel. The separator is generally electrically groundedtogether with the reaction chamber, but may be electrically floating orbiased. The shape of the separator is not limited as long as it preventsa diffusion of a gas in a direction of movement of a substrate but isnormally selected so that a complete barrier is provided for allcross-sections of the reaction chamber except for a gap between theseparating means and the moving substrate. If a member is located in thereaction chamber, the separator may have a shape by which only a passageof a gas left by that member is blocked. Usually however, the gap mustinclude a slit for diffusing a gas therethrough.

The number of separating plates and the distances therebetween depend ona desired profile in the direction of a layer thickness, of thecomposition of a layer to be deposited and is determined by experiment.

The locations of the gas inlet and outlet ports are also determinedexperimentally, depending on a desired profile, in the direction of alayer thickness, of the composition of a layer to be deposited. Forexample, if two layers having different compositions are desired, gasinlet ports for the respective reaction gases may be located at bothends of the reaction chamber in the direction of movement of asubstrate, respectively, and a common evacuation port locatedtherebetween. If a layer having a gradually changing composition profileis desired, the gas inlet ports for the respective reaction gases may belocated at both ends of the reaction chamber in the direction ofmovement of a substrate, respectively, and a common evacuation portlocated at one of the ends of reaction chamber. In this case, onereaction gas may be a doping gas, so that a layer having a graduallychanging concentration of a dopant in a direction of layer thickness canbe obtained.

According to this aspect of the present invention, a remarkablesimplification of a system for forming a plurality of layers using theroll-to-roll method may be advantageously attained. Also, it becomesadvantageously possible to provide a reactor for forming a layer inwhich the composition profile is controlled.

In another aspect of the present invention, there is provided a reactorfor depositing a layer on a moving substrate, said reactor comprising: areaction chamber having opposite ends; opposite electrodes for electricdischarge arranged in the reaction chamber, said substrate being movedbetween the opposite electrodes from one end to the other end of thereaction chamber; means for feeding a reaction gas into the reactionchamber; a power source for supplying a power between the oppositeelectrodes to excite the reaction gas to a plasma state, and a gridelectrode disposed between one of the opposite electrodes and the movingsubstrate at a given length from an end of the opposite electrodes nearsaid one end of the reaction chamber toward another end of the oppositeelectrodes near said other end of the reaction chamber, said gridelectrode having a width larger than the width of the moving substrate;whereby damage to the interface of the substrate and the deposited layerby plasma bombardment is prevented.

This aspect of the present invention is based on the following findings.If the high discharge power is applied to prepare a layer at a highdeposition rate, the energy conversion efficiency of the resultant solarcell is usually decreased. This is due to a deterioration of an i-typeamorphous silicon layer caused by contamination of this layer by amaterial sputtered from the underlying layer at the beginning of thedeposition of the i-type layer. This contamination is caused by plasmabombardment of the underlying layer at the beginning of the depositionof the i-type layer. After investigations into various methods ofdecreasing a plasma bombardment, it was found that arrangement of a gridelectrode between discharge electrodes near the entrance thereof maydecrease the plasma energy in the vicinity of the grid electrode andprevent the above-mentioned plasma damage while allowing a fastdeposition at a portion other than in the vicinity of the grid electrodewithout being affected by the grid electrode.

This aspect of the present invention was accomplished in connection withthe manufacture of an amorphous silicon solar cell, but it is clear thatthe present invention can be applied to other processes for depositing alayer on a substrate. That is, this aspect of the present invention isapplicable to a thin film device having a layer on a substrate (thesubstrate may have another layer on the top thereof). It is the factthat a damage to an interface between the layer and the substratemarkedly deteriorates the characteristics of the device while anexposure of the inner portion of the layer to such a high energy plasmahas an effect of accelerating the decomposition of a reaction gaswithout affecting the characteristics of the device.

The grid electrode of the present invention is arranged at only aportion of the parallel electrodes for glow discharge near the entranceof a substrate. The length of the grid electrode should be determined byexperiment because the role of grid electrode depends on thesemiconductor layer desired and bias voltage to be applied to the gridelectrode. However, in practice, the length of the grid electrode isappropriately selected to be within a half, for example, one third orless, of the entire length of the parallel electrodes for glow dischargefor obtaining a desired rate of deposition of a semiconductor layer. Thetype of grid electrode is selected from those comprising perforatedsheets having many pores throughout the entire sheet, including mesh ornet and comb forms. The size of the pore is selected such that plasmacan be enclosed,, but the passage of the activated species is maximized.The size of the pores can be practically selected to be within 50 meshin the case of a mesh or net form sheet.

In accordance with a further aspect of the present invention, there isprovided a reactor for depositing a layer on a moving substrate, thereactor comprising: a reaction chamber having opposite ends; oppositeelectrodes for electric discharge in the reaction chamber, the substratebeing moved between the opposite electrodes from one end to the otherend of the reaction chamber; means for feeding a reaction gas to thereaction chamber; a power source for supplying a power between theopposite electrodes to excite the reaction gas to a plasma state; a maskhaving an opening, disposed between one of the opposite electrodes andthe moving substrate, to limit an area whereat the layer is deposited onthe moved substrate, the mask being provided with a means for adjustingan electric field in the opening of the mask, whereby a layer having amodified distribution of the quality thereof is deposited on thesubstrate.

This aspect of the present invention was attained by the following. Froman investigation of the reasons why the quality of the layer isnonuniform when a mask is used, it was found that the electric field isconcentrated near the edge of the opening of the mask and a localdischarge is generated between the substrate and the edge portion of themask, resulting in a weakening of the discharge intensity near thecenter of the opening or the substrate.

Accordingly, the inventors experimented with various measures to levelthe distribution of the electric field in a portion of the mask opening,including: changing the shape of the edge of the mask opening, placingthe mask as near as possible to the substrate, and suppressing theapplied power, etc., not so as to disturb the profile of isoelectricplane. However, these measures were not satisfactory. Finally, anelectric-field-adjusting means which levels an applied potential profilewas provided at the center portion of the mask opening, so that theelectric field distribution had a uniform profile in the mask opening,and the problem was solved.

The electric field adjusting means used in the present invention is notparticularly limited as long as it makes the electric field profileuniform in the mask opening while maintaining the function of the maskopening, but wire members are preferable since they do not affect thelayer thickness distribution etc. but allow an effective adjustificationof the electric field. The wire member may be arranged in a simplecentral position in the opening, a parallel arrangement, a gridarrangement, with an appropriate space, etc., and preferably it isselected by experiment depending on the size and shape of the maskopening. The material of the electric-field-adjusting member is notlimited as long as it can concentrate an electric field in plasmadischarge and adjust an electric field in a mask opening, butelectrically conductive materials which can be easily machined arepreferable and metals with a low emission of a gas are more preferable,including stainless steel, tungsten, titanium, molybdenum, etc., whichare metals resistant to plasma.

In the formation of a microcrystalline amorphous silicon layer, a powerof at least 5 mW/cm² should be applied to the entire surface of asubstrate to obtain good electrical and physical properties. To meetthis requirement, the, electric-field-adjusting means preferablycomprises a wire member (including a filament and yarn) having adiameter of 0.5 to 2 mm, more preferably 1 to 1.5 mm.

Moreover, the electric field intensity may be selectively controlled byvarying a distance between the electric-field-adjusting means and thesubstrate.

The shape of the discharge electrodes to which a mask provided with theabove electric-field-adjusting means can be applied, may be the parallelplane type, the parallel curved plane type including a can, andnon-parallel electrodes. For non-parallel electrodes, the shape,location, material, etc., of an electric-field-adjusting means may beselected to make the electric field profile uniform.

In accordance with the foregoing description the present invention,provides a system for manufacturing a semiconductor device by depositinga first layer on a substrate in a first reactor, and depositing a secondlayer on the first layer on the substrate in a second reactor, and thendepositing a third layer on the second layer above the substrate in athird reactor, the substrate being transferred from the first to thesecond to the third reactors,

(A) said first reactor comprising:

(i) a first reaction chamber having first and second ends;

(ii) first and second electrodes for electrical discharge arranged inthe first reaction chamber, the substrate being moved between the firstand second electrodes from the first to second ends of the firstreaction chamber;

(iii) a first mask means having an opening, disposed between the secondelectrode and the moving substrate, for limiting an area whereat thefirst layer is deposited on the moving substrate;

(iv) first means for feeding a first reaction gas into the firstreaction chamber; and

(v) a first power source for supplying a power between the first andsecond electrodes to excite the first reaction gas to a plasma state;

(B) said second reactor comprising:

(i) a second reaction chamber having third and fourth ends, the thirdend of the second reaction chamber being connected with the second endof the first reaction chamber;

(ii) third and fourth electrodes for electric discharge arranged in thesecond reaction chamber, the substrate having the first layer thereonbeing moved between the third and fourth electrodes from the third tofourth ends of the second reaction chamber;

(iii) means for feeding a second reaction gas into the second reactionchamber;

(iv) means for separating at least the space between the moved substrateand the fourth electrode into a plurality of regions and substantiallypreventing a diffusion of a gas between the separated regions; and

(v) a second power source for supplying a power between the third andfourth electrodes to excite the second reaction gas to a plasma state;and

(C) a third reactor comprising:

(i) a third reaction chamber having fifth and sixth end, the fifth endof the third reaction chamber being connected to the fourth end of thesecond reaction chamber;

(ii) fifth and sixth electrodes for electric discharge arranged in thethird reaction chamber, the substrate having the first and second layersthereon being moved between the fifth and sixth electrodes from thefifth to sixth ends of the third reaction chamber;

(iii) a second mask means having an opening, disposed between the sixthelectrode and the moving substrate, for limiting an area whereat thethird layer is deposited on the moving substrate, at least one of saidfirst and second mask means being provided with means for adjusting anelectric field in the opening of the mask;

(iv) third means for feeding a third reaction gas into the thirdreaction chamber; and

(v) a third power source for supplying a power between the fifth andsixth electrodes to excite the third reaction gas to a plasma state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a system for manufacturing asolar cell having a p-i-n structure in the roll-to-roll method inaccordance with the present invention;

FIG. 2 is a sectional view of the solar cell manufactured by the systemof FIG. 1;

FIG. 3 is a view of a separator provided in the system of FIG. 1;

FIG. 4 illustrates a profile of boron in an i-type layer obtained byexperiments;

FIG. 5 is a perspective view of an example of a construction of theelectrodes and separators;

FIG. 6 is a sectional view of a reactor having a grid electrode betweendischarge electrodes;

FIG. 7 illustrates the relationships of the deposition rate and energyconversion efficiency to the discharge power;

FIGS. 8 and 9 are sectional views of reactors provided with separatorsand a grid electrode;

FIG. 10 is a schematic view of a construction of discharge electrodeswith a mask having an opening;

FIG. 11 illustrates a mask having an opening without anelectric-field-adjusting means;

FIG. 12 illustrates a mask having an opening and provided with anelectric-field-adjusting means; and

FIG. 13 shows a relationship of the conductivity of a deposited layerobtained in an experiment to the applied discharge power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a system for continuously manufacturing an amorphoussilicon solar cell, as an example of the present invention.

The basic constitution of this apparatus is the same as that of JapaneseUnexamined Patent Publication (Kokai) Nos. 58-216475 and 59-34668, thedescriptions of which are incorporated herein by reference.

In FIG. 1, reaction chambers 1, 2 and 3 are used for depositing p-type,i-type (intrinsic), and n-type amorphous silicon semiconductor layers. Acontinuous substrate 17, for example, a flexible polyester resin filmwhich has a laminate of aluminum and stainless steel bilayer as a bottomelectrode, is transferred from a supply chamber 18 to a take-up chamber19 through the first, second, and third reaction chambers 1, 2, and 3,which are respectively connected through buffer chambers 13 for gasisolation. Reference numerals 4 to 9 denote discharge electrodes, andreference numeral 10 denotes a radio frequency power source forsupplying a radio frequency power, typically 13, 56 MHz, to thedischarge electrodes 4 to 9.

In each reaction chamber 1, 2 or 3, silane (SiH₄) gas is fed from a gasinlet port 15 and decomposed at a given temperature in a plasmadischarge atmosphere to deposit silicon onto the substrate 17. In thefirst reaction chamber 1, a p-type doping gas, e.g., diborane (B₂ H₆),is fed with the silane gas to dope a p-type dopant (boron) in thedeposited silicon layer. In the third reaction chamber 3, an n-typedoping gas, e.g., phosphine (PH₃), is fed to form a silicon layer dopedwith phosphorus, an n-type dopant. Thus, while the substrate 17 istransferred from a supply roll 20 in the supply roll chamber 18 to atake-up roll 21 in the take-up chamber 19, through the reaction chambers1, 2 and 3, a p-type amorphous silicon layer 31, an i-type amorphoussilicon layer 32, and an n-type amorphous silicon layer 33 aresuccessively deposited on the substrate 17, thus forming a p-i-n layeredstructure of a solar cell (see FIG. 2). When necessary, a mask 22 isplaced between the discharge electrodes 5 and 9 and the substrate 17 inthe first and third reaction chambers 1 and 3 to control the layerthickness of the p-type and n-type silicon layers in this roll-to-rollmethod.

As described before, control of a p-type dopant in an i-type siliconlayer is preferably to attain a high efficiency of energy conversion ofa solar cell, which should be done in the second reaction chamber 2. Theproblem of plasma damage of the interface between the i-type andunderlying p-type silicon layers occurs in the reaction chamber 2. Theproblem concerning the use of a mask to control the quality and layerthickness of a deposited layer occurs in the first and third reactionchambers 1 and 3, when such a mask is used.

According to the present invention, separators 11 are arranged betweenthe discharge electrodes 6 and 7 in the second reaction chamber 2 toattain a desired profile of a dopant concentration in an i-type siliconlayer. Also in the second reaction chamber 2, a grid electrode 23 ispreferably arranged between the discharge electrodes 6 and 7 only at aportion near the first reaction chamber 1, so that a high power can beapplied to the discharge electrodes 6 and 7 to increase the depositionrate of silicon without causing plasma damage to the interface betweenthe i-type and p-type silicon layers. An electric-field-adjusting meanssuch as a metal wire is provided for the mask 22 in the first and thirdreaction chambers 1 and 3, to make the electric field profile uniform inan opening of the mask 22.

According to the above features of the present invention, an amorphoussilicon solar cell having an improved energy conversion efficiency canbe manufactured at a high deposition rate.

Each reaction chamber is now described in more detail.

One example of a second reaction chamber 2 for forming an i-typeamorphous silicon semiconductor layer 32 had the following construction.Between opposite discharge electrodes 6 and 7, five separators 11 werearranged perpendicular to the electrodes 6 and 7. FIG. 3 is a sectionalview of the reaction chamber 2 and illustrates the shape of theseparator 11. The separator 11 separated a space between the dischargeelectrodes 6 and 7 into a plurality of regions and acted as a barrierfor the regions in all of the sections of the reaction chamber 2 exceptfor slight gaps 14 between the separators 11 and the substrate 17 or thedischarge electrodes 6 and 7. As a result, a reaction gas fed from angas inlet port 15 at the downstream end, in the direction of movement ofthe substrate, of the reaction chamber 2 must have passed through thegaps 14 to reach an outlet port 16 at the opposite upstream end of thereaction chamber 2.

The separators 11 were arranged at a slight distance from the respectivedischarge electrodes 6 and 7 to form gaps 14 therebetween. The gaps 14were formed to allow the passage of a reaction gas, to insulate theseparators 11 from the power electrode 7, and to allow the passage ofthe substrate 17 near the electrically grounded electrode 6. The 14provided a distance of 3 mm between the separators 11 and the respectiveelectrodes 6 and 7. The separators 11 may be made of either anelectrically conductive or insulating material but should be a materialwhich does not release an impurity in the plasma. In this example, theseparators 11 were made of stainless steel and were electricallygrounded to the earth.

The substrate 17 was a 100 μm-thick polyethylene telephthalate film onwhich a 300 nm-thick aluminum layer and a 5 nm-thick stainless steellayer were laminated. A p-type amorphous silicon layer 31 had beenalready deposited in the first reaction chamber 1 from a reaction gas ofsilane mixed with diboran (B₂ H₆) and the p-type silicon layer 31 had athickness of 26 to 30 nm on the substrate 17. An n-type amorphoussilicon layer 33 to be deposited in the third reaction chamber 3 from areaction gas of silane mixed with phosphine (PH₃) and the n-type siliconlayer 33 would have the same thickness as that of the p-type siliconlayer 31. An i-type or intrinsic amorphous silicon layer 32 wasdeposited in the second reaction chamber 2 from silane gas without anydoping gas and had a thickness of about 500 nm. As the thickness of thelayers 31 to 33 to be deposited were different but the speed of movementof the substrate should be the same in the system in FIG. 1, the poweroutput of the radio frequency power source, the size of the dischargeelectrodes, the amount of feed gas, the temperatures of the dischargeelectrodes, and the pressures in the reaction chambers, etc., wereadjusted to attain the desired thicknesses of the layers deposited.

The reaction gas of silane was fed to the reaction chamber 2 from thegas inlet port 15 near the third reaction chamber 3 and evacuated fromthe gas outlet port 16 near the first reaction chamber 1.

A solar cell having a p-i-n structure was manufactured under theconditions described above, but a grid electrode 23 was not used in thisexample. The depth profile of boron atom of the thus-obtained solar cellwas examined by secondary ion mass spectroscopy (SIMS). The result isshown in FIG. 4 as the solid line A, with the result of a comparativeexample as the broken line B in which a solar cell having the same layerstructure as that of the above example was manufactured under the sameconditions except using a conventional system, i.e., without separators.Here, note that it is known that, in the roll-to-roll method as in thesystem in FIG. 1, slight amounts of B₂ H₆ and PH₃ gases usuallypenetrate the second reaction chamber 2 from the adjacent reactionchambers 1 and 3 through the buffer chambers 13, and that this isunavoidable. Therefore, a boron concentration profile can be seen in thei-type silicon layer 32 in FIG. 4.

It is seen from FIG. 4 that, in the case of the conventional systemwithout separators, the boron gas from the first reaction chamber 1 wasdiffused uniformly throughout the reaction chamber 2, resulting in aflat boron atom concentration profile in the direction of the layerthickness of the i-type layer 32. On the other hand, in the case of theexample of the present invention using separators, the boron atomconcentration profile is abrupt at the interface between the p-type andi-type layers 31 and 32 and has a constant decline in the i-type layer.It is known that an energy conversion efficiency of an amorphous siliconsolar cell may be improved by having a gradual doping concentrationdistribution in an i-type silicon layer. (see, for example, P.Sichanugrist et al "High Performance a-Si:H Solar Cells Prepared fromSiH₄ at High Deposition Rates", Technical Digest of the InternationalPVSEC-2, Kobe, Japan, P-I-16, pp 187-190, Nov. 13-16/1984). Actually, asolar cell manufactured in accordance with a process of the presentinvention had improved characteristics as seen in the following table inwhich characteristics of a comparative solar cell manufactured in asimilar process of the prior art, that is, without separators, are alsoincluded.

                  TABLE                                                           ______________________________________                                                      Value                                                                           Invention Comparison                                                          (with     (without                                            Performance     separators)                                                                             separators)                                         ______________________________________                                        Open circuit voltage                                                                          0.90      0.89                                                V.sub.OC [V]                                                                  Short-circuit current                                                                         14.0      12.7                                                density [mA/cm.sup.2 ]                                                        Fill factor     0.71      0.65                                                Energy conversion                                                                             9.0       7.4                                                 efficiency [%]                                                                ______________________________________                                    

The above results demonstrate that, by separating a plasma space in areaction chamber into regions and preventing gas diffusion to theregions as much as possible, the composition of the reaction gas may becontrolled such as having a distribution or profile in a reactionchamber from one end to another end thereof. Thus, according to thepresent invention, a desired distribution of a reaction gas can beattained.

FIG. 5 illustrates a modification of a reaction chamber 2 in the systemshown in FIG. 1. In this embodiment, a reaction gas is fed through adischarge electrode 7' into respective separated regions between thedischarge electrodes 6 and 7'. The electrode 7' has many pores 25 at thesurface thereof, through which a reaction gas is fed to the respectiveregions, and contains a gas diffusing plate 26 by which the reaction gasfed from a gas inlet port 16' is distributed throughout the electrode7'.

Next, the effects of a grid electrode in a reactor were examined asshown in FIG. 6, which shows a part of the reaction chamber 2' of thesystem of FIG. 1. In this reaction chamber 2', however, the separators11 were not used and a discharge electrode 7' as shown in FIG. 5 wasused in place of the discharge electrode 7 in FIG. 1. Further, a gridelectrode 23 was arranged between the discharge electrodes 6 and 7'. Thegrid electrode 23 was disposed along a substrate 17 and covered the fullwidth of the substrate 17 and about one third of the length of thedischarge electrodes 6 and 7' in the direction of movement of asubstrate 17 from the end of the electrodes 6 and 7' where the substrate17 was introduced. The grid electrode 23 was capable of being suppliedwith a bias voltage (e.g., +200 V to -200 V) by a DC power source 12.The grid electrode 23 was made of stainless steel and was a mesh havinga mesh size of 200.

The substrate 17 was the same as that used in the former example. Thestructure of the layers of a solar cell was also the same as in theformer example. But the discharge power, the speed of movements of asubstrate, and the pressure of the reaction gases, etc., were controlledto obtain the same structure of the layers. The grid electrode 23 wasspaced from the substrate 17 by a distance of 25 mm and the distancebetween the discharge electrodes 6 and 7' was 50 mm.

In this system, solar cells were manufactured with a bias of -20 Vapplied to the grid electrode 23 and various radio frequency powersapplied to the discharge electrodes 6 and 7'. The deposition rates inthis experiment is shown as the solid line A in FIG. 7. Of course, withthe increase of the discharge power, the deposition rate also increased,as seen in FIG. 7. The characteristics of the resultant solar cells,i.e., energy conversion efficiencies of the solar cells, were thenexamined in relation to the discharge power. The results thereof areshown also in FIG. 7 as the solid line A'. In comparison, very similarsolar cells were manufactured as above except that the grid electrode 23was removed from the reaction chamber 2'. The energy conversionefficients of the resultant solar cells were also examined and are shownin FIG. 7 as the broken line B', together with the broken line B for thedeposition rate. Moreover, very similar solar cells were againmanufactured with a grid electrode covering the entire width and lengthof the discharge electrodes 6 and 7' in the reaction chamber 2'. Theresults thereof are shown in FIG. 7 as the dotted line C.

As seen in FIG. 7, in an example of the present invention, i.e., using agrid electrode, the energy conversion efficiency of the solar cell wasnot decreased although the discharge power or the deposition rate wasincreased. In contrast, in a conventional system, i.e., without a gridelectrode, the energy conversion efficiency of the solar cell wasdecreased with an increase of the discharge power or the depositionrate. In case of the grid electrode covering the entire width and lengthof the discharge electrode, the deposition rate was not increased evenif the discharge power was increased.

FIGS. 8 and 9 illustrate examples of a reactor for depositing asemiconductor layer, in which a combination of separators and a gridelectrode described above is used. In FIG. 8, separators 11 are arrangedbetween the discharge electrodes 6 and 7' as in FIG. 1, i.e., throughoutthe space between the discharge electrodes 6 and 7' and a grid electrode23 is arranged as in FIG. 6, i.e., between the discharge electrodes 6and 7' only at a portion (one third) of the discharge electrodes 6 and7' near the entrance of a substrate 17. In this example, the gridelectrode 23 overlaps some of the separators and generally should beelectrically insulated from the separators, usually by spacing the gridelectrode 23 from the separators 11. In FIG. 9, a grid electrode 23 isarranged as in FIG. 6 and separators 11' are arranged only at theremaining portion of the space between the discharge electrodes, i.e.,following the grid electrode 23 in the direction of movement of asubstrate.

Now, regarding the first or third reaction chamber 1 or 3 of the systemof FIG. 1, the effect of an electric-field-adjusting means provided witha mask opening was confirmed by the following example.

FIG. 10 shows an inner construction of a reactor used in theexperiments, in which reference numeral 41 denotes an electrode which iselectrically grounded, reference numeral 42 denotes a substrate of apolymer film which is continuously moved in the direction of the arrow,reference numeral 43 denotes a mask having an opening 43a (50 mm longand 250 mm wide) for controlling the thickness of a deposited layer,reference numeral 44 denotes a plasma, reference numeral 45 denotes ahigh frequency discharge electrode, and reference numeral 46 denotes aradio frequency power source for the electrodes 41 and 45, the frequencyof the radio frequency discharge power being 13.56 MHz.

In this reactor, with a conventional mask as shown in FIG. 11, i.e.,without an electric-field-adjusting means, an n-type amorphous siliconsemiconductor layer was deposited from a reaction gas of a mixture ofhydrogen, silane and phosphine. The pressure in the reaction chamber was1 Torr, the temperature of the substrate 42 was 160° C., the dischargepower applied was 0.05 W/cm², and the substrate 42 was stopped for 30minutes. It was confirmed that, although a portion of the depositedsilicon semiconductor layer near the edge of the opening 43a wasmicrocrystalline having a conductivity of about 5S·cm⁻¹, the centralportion of the deposited silicon semiconductor layer had a considerablylower conductivity of 9 × 10⁻⁴ S·cm⁻¹, which indicated that the centralportion of the deposited layer was completely amorphous, notmicrocrystallized.

Next, a mask provided with a wire at the center of the opening 43a ofthe mask 43, the wire crossing the opening 43a as shown in FIG. 12, wasused as an electric-field-adjusting means and an n-type siliconsemiconductor layer was deposited under the same condition as aboveexcept for the applied power. The applied discharge power varied from0.01 to 0.04 W/cm². The wire was stainless steel and had a diameter of 1mm.

FIG. 13 shows the conductivity of the resultant deposited siliconsemiconductor layer at the center portion of the opening 43a. In FIG.13, white circles indicates a value measured under a light and blackcircles indicate a value measured in the dark. From these results, itwas confirmed that even the central portion of the deposited siliconsemiconductor layer was completely microcrystallized when a metal wireis provided at the mask opening. It was also confirmed that thedeposited silicon semiconductor layer was a uniform microcrystallinefilm throughout the mask opening. As a result, the characteristics ofthe silicon semiconductor layer were desirably improved in comparisonwith those obtained in a conventional reactor.

Furthermore, according to the present invention, i.e., using anelectric-field-adjusting means, it was also seen that a deposited layercan be microcrystallized by a low power density, such as about 0.02W/cm², one half of a conventionally used power density. Note thatdistribution of the thickness obtained by this method were very uniformas compared with a conventional method, and thus no problem arose.

In general mask with an opening is used for control of the quality oflayer thickness of the layer. The above experiment demonstrated that theelectric field in an opening of a mask used between a substrate and oneof the discharge electrodes can be made uniform by providing anelectric-field-adjusting means at the mask opening, which allows auniform deposited layer to be obtained. This is obviously advantageouseven if a deposited layer is amorphous and not microcrystalline.

Returning to FIG. 1, in accordance with the system of the presentinvention, which includes masks 22 with an electric-field-adjustingmeans (such as the means 47 in FIG. 12) in the first and third reactionchambers 1 and 3; and separators 11 and a grid electrode 23 in thesecond reaction chamber, a solar cell having a p-i-n structure can becontinuously manufactured on a flexible polymer film with an increaseddeposition rate without deterioration of the characteristics of a solarcell, but with an improved characteristic such as an energy conversionefficiency of a solar cell. The present invention apparently may be alsoapplied to a solar cell having an n-i-p structure, a p-i-n/p-i-n tandemstructure or other structures, as well as any other multilayersemiconductor device. Note that the present invention is advantageouswhen a reactor is provided with any of separators and a grid electrodeand, when the reactor includes a mask having an opening and anelectric-field-adjusting means.

We claim:
 1. A reactor for depositing a layer on a moving substrate,said reactor comprising:a reaction chamber having opposite ends;opposite electrodes for electric discharge arranged in the reactionchamber, means for moving said substrate between the opposite electrodesfrom one end to the other end of the reaction chamber; first means forfeeding a reaction gas into the reaction chamber; means for separatingat least the space between the moved substrate and one of the oppositeelectrodes into a plurality of regions and substantially preventing adiffusion of a gas between the separated regions; and a power source forsupplying power between the opposite electrodes to excite the reactiongas to a plasma state; whereby a layer having a modified depthcomposition profile may be deposited on the substrate.
 2. A reactoraccording to claim 1, wherein said separating means acts as a barrierfor all cross-sections of the reaction chamber except for a gap betweensaid separating means and the moving substrate.
 3. A reactor accordingto claim 1, wherein said first gas feeding means feeds the reaction gasat one of said opposite ends of the reaction chamber and the gas in thereaction chamber is evacuated near the other end of said opposite endsof the reaction chamber.
 4. A reactor, according to claim 3, furthercomprising a second means for feeding gas into the reaction chamber atsaid other end of said opposite ends of the reaction chamber.
 5. Areactor according to claim 1, wherein said one of said oppositeelectrode acts as said first gas feeding means and feeds the reactiongas into each region separated by said separating means.
 6. A reactor,according to claim 5, further comprising a second means for feeding agas into the reaction chamber at said other end of said opposite ends ofthe reaction chamber.
 7. A reactor according to claim 6, wherein saidsecond means is for feeding a gas feeds a doping gas.
 8. A reactoraccording to claim 1, wherein said substrate is a flexible strip and istransferred from a supply roll to a take-up roll through said reactionchamber, during which transfer the layer is deposited on the substrate.9. A reactor according to claim 1, for depositing an amorphous siliconlayer.
 10. A reactor according to claim 1, further comprising: a gridelectrode disposed between one of the opposite electrodes and the movingsubstrate at a given length from an end of the opposite electrodes nearsaid one end of the reaction chamber toward another end of the oppositeelectrodes near said other end of the reaction chamber, said gridelectrode having a width larger than the width of the moving substrate;whereby a layer having a modified depth composition profile is depositedon the substrate and damage to the interface of the substrate anddeposited layer by plasma bombardment is minimized.
 11. A reactoraccording to claim 10, wherein said layer to be deposited is asemiconductor layer and said substrate already has on the top thereofanother semiconductor layer of a different semiconductor from saidsemiconductor to be deposited.
 12. A reactor according to claim 11,wherein said semiconductor layer to be deposited is an i-type siliconsemiconductor and said another semiconductor layer is selected from thegroup consisting of p-type and n-type silicon semiconductors.
 13. Areactor according to claim 10, wherein said grid electrode is a porousmetal plate.
 14. A reactor according to claim 10, wherein said gridelectrode is a metal mesh screen.
 15. A reactor according to claim 10,wherein said grid electrode has a length of less than half of the lengthof the opposite electrodes.
 16. A reactor for depositing a layer on amoving-substrate, comprising:a reaction chamber having opposite ends;opposite electrodes for electric discharge arranged in the reactionchamber, means for moving said substrate between the opposite electrodesfrom one end to the other end of the reaction chamber; means for feedinga reaction gas into the reaction chamber; a power source for supplyingpower between the opposite electrodes to excite the reaction gas to aplasma state; a mask means having an opening, disposed between one ofsaid opposite electrodes and the moving substrate, for limiting an areawhere said layer is deposited on the moved substrate, said mask meansbeing provided with means for adjusting an electric field in the openingof the mask, whereby a layer having a modified distribution of thequantity thereof is deposited on the substrate.
 17. A reactor accordingto claim 16, wherein said electric field adjusting means is a metal wireextending transverse at the center of the opening of said mask means inrelation to the direction of the movement of the substrate, so that theelectric field in the opening of the mask can be made uniform.
 18. Areactor according to claim 16, wherein said substrate is a flexiblestrip transferred from a supply roll to a take-up roll through saidreaction chamber.
 19. A reactor according to claim 16, wherein saidreactor is for uniformly depositing a microcrystalline siliconsemiconductor layer on the substrate.
 20. A reactor according to claim16, for manufacturing an amorphous silicon solar cell.
 21. A reactor fordepositing a layer on a moving substrate, said apparatus comprising:areaction chamber having opposite ends; opposite electrodes for electricdischarge arranged in the reaction chamber means for moving saidsubstrate between the opposite electrodes from one end to the other endof the reaction chamber; means for feeding a reaction gas into thereaction chamber; a power source for supplying power between theopposite electrodes to excite the reaction gas to a plasma state, and agrid electrode disposed between one of the opposite electrodes and themoving substrate along a portion of the length from an end of theopposite electrodes near said one end of the reaction chamber towardanother end of the opposite electrodes near said other end of thereaction chamber, said grid electrode having a width larger than thewidth of the moving substrate; whereby damage to the interface of thesubstrate and the deposited layer by plasma bombardment is minimized.22. A reactor according to claim 21, wherein said layer to be depositedis a semiconductor layer and said substrate already has on the topthereof another semiconductor layer of a different semiconductor fromsaid semiconductor to be deposited.
 23. A reactor according to claim 22,wherein said semiconductor layer to be deposited is an i-type siliconsemiconductor and said another semiconductor layer is selected from thegroup consisting of p-type and n-type silicon semiconductors.
 24. Areactor according to claim 21, wherein said grid electrode is a porousmetal plate.
 25. A reactor according to claim 21, wherein said gridelectrode is a metal mesh screen.
 26. A reactor according to claim 21,wherein said grid electrode has a length of less than half of the lengthof the opposite electrodes.
 27. A system for manufacturing asemiconductor device by depositing a first layer on a substrate in afirst reactor, and depositing a second layer on the first layer on thesubstrate in a second reactor and then depositing a third layer on thesecond layer above the substrate in a third reactor, the substrate beingtransferred from the first to the second to the third reactors,(A) saidfirst reactor comprising:(i) a first reaction chamber having first andsecond ends; (ii) first and second electrodes for electrical dischargearranged in the first reaction chamber, the substrate being movedbetween the first and second electrodes from the first to second ends ofthe first reaction chamber; (iii) a first mask means having an opening,disposed between the second electrode and the moving substrate, forlimiting an area whereat the first layer is deposited on the movingsubstrate; (iv) first means for feeding a first reaction gas into thefirst reaction chamber; and (v) a first power source for supplying apower between the first and second electrodes to excite the firstreaction gas to a plasma state; (B) said second reactor comprising:(i) asecond reaction chamber having third and fourth ends, the third end ofthe second reaction chamber being connected with the second end of thefirst reaction chamber; (ii) third and fourth electrodes for electricdischarge arranged in the second reaction chamber, the substrate havingthe first layer thereon being moved between the third and fourthelectrodes from the third to fourth ends of the second reaction chamber;(iii) means for feeding a second reaction gas into the second reactionchamber; (iv) means for separating at least the space between the movedsubstrate and the fourth electrode into a plurality of regions andsubstantially preventing a diffusion of a gas between the separatedregions; and (v) a second power source for supplying a power between thethird and fourth electrodes to excite the second reaction gas to aplasma state; and (C) a third reactor comprising:(i) a third reactionchamber having fifth sixth end, the fifth end of the third reactionchamber being connected to the fourth end of the second reactionchamber; (ii) fifth and sixth electrodes for electric discharge arrangedin the third reaction chamber, the substrate having the first and secondlayers thereon being moved between the fifth and sixth electrodes fromthe fifth to sixth ends of the third reaction chamber; (iii) a secondmask means having an opening, disposed between the sixth electrode andthe moving substrate, for limiting an area whereat the third layer isdeposited on the moving substrate, at least one of said first and secondmask means being provided with means for adjusting an electric field inthe opening of the mask; (iv) third means for feeding a third reactiongas into the third reaction chamber; and (v) a third power source forsupplying a power between the fifth and sixth electrodes to excite thethird reaction gas to a plasma state.
 28. A system according to claim27, said second reactor further comprising(vi) a grid electrode disposedbetween the fourth electrode and the moved substrate along a givenlength from an end of the third and fourth electrodes near the third endof the second reaction chamber toward another end of the third andfourth electrodes near the fourth end of the second reaction chamber,the grid electrode having a width larger than the width of the movedsubstrate.
 29. A system according to claim 27, wherein said electricfield adjusting means is a metal wire extending transverse at the centerof the opening of said mask means in relation to the direction of themovement of the substrate.
 30. A system according to claim 27, formanufacturing a silicon semiconductor solar cell having a structureselected from the group consisting of p-i-n and n-i-p structures.
 31. Asystem according to claim 27, wherein at least one of said first andthird silicon semiconductor layers is microcrystalline and the remaininglayers are non-crystalline.